Carbon fiber nonwoven fabric

ABSTRACT

A carbon fiber nonwoven fabric in which carbon fibers are sized with an aliphatic compound having a plurality of epoxy groups or a specific aromatic compound; the number average x of carbon fibers forming a carbon fiber bundle, in which the number of carbon fibers forming the carbon fiber bundle is 90 or more, is 90 to 1,000 fibers per bundle among the carbon fiber bundles in the carbon fiber nonwoven fabric; and the standard deviation σ of the number of carbon fibers forming the carbon fiber bundle is 50 to 500.

TECHNICAL FIELD

This disclosure relates to a carbon fiber nonwoven fabric and, specifically, to a carbon fiber nonwoven fabric which can satisfy both of high flowability and mechanical properties when a molded article of a carbon fiber composite material is made using the same.

BACKGROUND

A carbon fiber composite material comprising carbon fibers and a thermoplastic resin is used for manufacture of various molded articles, and various technologies, having high mechanical properties of a manufactured molded article and a good flowability at the time of the manufacture, have been proposed. Among those, by forming carbon fibers in the carbon fiber composite material as a formation of a nonwoven fabric, for example, in JP 2012-158846 A, a carbon fiber nonwoven fabric is proposed wherein the proportion of specified carbon fiber bundles in a carbon fiber nonwoven fabric relative to the whole amount of fibers is suppressed, and the average number of fibers in the respective specified carbon fiber bundles is controlled in a specified range.

However, in such a carbon fiber nonwoven fabric as described in JP 2012-158846 A wherein the carbon fiber bundles in the carbon fiber nonwoven fabric are thin, the proportion of bundles is few and the carbon fibers are spread, although the mechanical properties of a molded article of a carbon fiber composite material manufactured using the same are excellent, flowability at the time of molding is low and moldability is poor. This is because the carbon fibers, which are reinforcing fibers, are sufficiently distributed. Therefore, stress is hard to be concentrated and the reinforcing effect due to the carbon fibers is sufficiently exhibited. On the other hand, the carbon fibers are crossed to each other to restrict their movements and therefore the carbon fibers become hard to be moved.

In JP 2012-158847 A, a composite material is proposed wherein the proportion of specified carbon fiber bundles in a carbon fiber nonwoven fabric relative to the whole amount of fibers, similar to that described above, is set higher, and the average number of fibers in the respective specified carbon fiber bundles is controlled in another specified range. However, in such a carbon fiber nonwoven fabric as described in JP 2012-158847 A wherein the carbon fiber bundles are thick and the proportion of the bundles is many, although flowability at the time of manufacturing a molded article of a carbon fiber composite material using the same is high and moldability is excellent, the mechanical properties are low and the variations in the mechanical properties are great. This is because the impregnation property of a resin into the carbon fiber bundles because the bundles are thick, and stress is liable to be concentrated to end portions of the carbon fibers, but the carbon fibers are easily moved because the carbon fibers do not form networks.

Accordingly, it could be helpful to provide a carbon fiber nonwoven fabric in which high flowability and mechanical properties can be both satisfied with small variability in mechanical properties when a carbon fiber composite material is molded, and which also has an excellent shaping property for a carbon fiber mat.

SUMMARY

We thus provide:

(1) A carbon fiber nonwoven fabric including carbon fibers, characterized in that the carbon fibers are sized with an aliphatic compound having a plurality of epoxy groups, a number average x of carbon fibers forming a carbon fiber bundle (1), in which a number of carbon fibers forming a carbon fiber bundle is 90 or more, is 90 to 1,000 fibers per bundle among carbon fiber bundles in the carbon fiber nonwoven fabric, and a standard deviation σ of the number of carbon fibers forming the carbon fiber bundle (1) is 50 to 500.

(2) A carbon fiber nonwoven fabric including carbon fibers, characterized in that the carbon fibers are sized with an aromatic compound having a plurality of epoxy groups in which a number of atoms present between an epoxy group and an aromatic ring is 6 or more, a number average x of carbon fibers forming a carbon fiber bundle (1), in which a number of carbon fibers forming a carbon fiber bundle is 90 or more, is 90 to 1,000 fibers per bundle among carbon fiber bundles in the carbon fiber nonwoven fabric, and a standard deviation σ of the number of carbon fibers forming the carbon fiber bundle (1) is 50 to 500.

(3) The carbon fiber nonwoven fabric according to (1) or (2), wherein the compound having a plurality of epoxy groups is a compound having an epoxy group at each end of the longest atomic chain.

(4) The carbon fiber nonwoven fabric according to (3), wherein the compound having a plurality of epoxy groups is a compound having an epoxy group only at each end of the longest atomic chain.

(5) The carbon fiber nonwoven fabric according to (1) or (3), wherein a number of atoms of the longest atomic chain of the aliphatic compound having a plurality of epoxy groups is 20 to 200.

(6) The carbon fiber nonwoven fabric according to any of (1), (3) to (5), wherein the aliphatic compound having a plurality of epoxy groups is at least one kind of compound selected from glycerol polyglycidyl ether, diglycerol polyglycidyl ether, polyethylene glycol diglycidyl ether group and polypropylene glycol diglycidyl ether group.

(7) The carbon fiber nonwoven fabric according to (2), wherein the aromatic compound having a plurality of epoxy groups in which a number of atoms present between an epoxy group and an aromatic ring is 6 or more is a compound shown in chemical formula (1):

wherein R¹ is chemical formula (2):

R² represents an alkylene group having a carbon number of 2 to 30, R³ is —H or —CH₃, m and n represent an integer of 2 to 48, and m+n is 4 to 50.

(8) The carbon fiber nonwoven fabric according to (7), wherein the R² is —CH₂CH₂— or —CH(CH₃) CH₂—.

(9) The carbon fiber nonwoven fabric according to (2), wherein the aromatic compound is a condensed polycyclic aromatic compound.

(10) The carbon fiber nonwoven fabric according to (9), wherein a skeletal structure of the condensed polycyclic aromatic compound is naphthalene, anthracene, phenanthrene or pyrene.

(11) A carbon fiber nonwoven fabric including carbon fibers, characterized in that at least one kind of compound selected from chemical formulae (3), (4) and (5) shown in chemical formulae (3) to (5) is made to adhere to the carbon fibers at an amount of 0.1 to 5.0 wt. % relative to the weight of the carbon fibers of 100 wt. %, a number average x of carbon fibers forming a carbon fiber bundle (1), in which a number of carbon fibers forming a carbon fiber bundle is 90 or more, is 90 to 1,000 fibers per bundle among carbon fiber bundles in the carbon fiber nonwoven fabric, and a standard deviation σ of the number of carbon fibers forming the carbon fiber bundle (1) is 50 to 500:

In the above-described formulae, R₁ represents H, OH, formulae (6) or (7), R₂ represents H or OH, m and n represent an integer of 1 to 49, and m+n is 10 to 50:

(12) The carbon fiber nonwoven fabric according to any of (1) to (11), wherein the standard deviation σ of the number of carbon fibers forming the carbon fiber bundle (1) is 50 to 350.

(13) The carbon fiber nonwoven fabric according to any of (1) to (12), wherein a proportion of the carbon fiber bundles (1) relative to the total weight of carbon fibers is 5 to 80 wt. %.

(14) The carbon fiber nonwoven fabric according to any of (1) to (13), wherein the carbon fiber nonwoven fabric is formed from a carbon fiber bundle whose drape value (cm)/single fiber flexural stiffness (Pa·cm⁴) at 25° C. is 1.4×10³ to 4.0×10³ (cm/(Pa·cm⁴)).

(15) The carbon fiber nonwoven fabric according to any of (1) to (14), wherein a single fiber flexural stiffness of carbon fibers forming the carbon fiber nonwoven fabric is 1.0×10⁻¹¹ to 2.8×10⁻¹¹ (Pa·cm⁴).

(16) The carbon fiber nonwoven fabric according to any of (1) to (15), wherein a fiber length Ln of carbon fibers forming the carbon fiber nonwoven fabric is 3 to 50 mm.

In such a carbon fiber nonwoven fabric, by satisfying the above-described ranges, as shown in the results of Examples described later, a high flowability at the time of molding using it can be obtained as well as high mechanical properties of a molded article can be realized, variability in the mechanical properties is small, and an excellent shaping property can be exhibited. Further, to satisfy both of high flowability and mechanical properties more securely, as described above, can be employed preferred compound, standard deviation σ of the number of carbon fibers, range of the proportion of the carbon fiber bundles (1) relative to the total weight of carbon fibers, range of the drape value (cm)/single fiber flexural stiffness (Pa·cm⁴), range of the single fiber flexural stiffness of carbon fibers.

Thus, in the carbon fiber nonwoven fabric, a carbon fiber nonwoven fabric can be provided wherein, when a carbon fiber composite material is molded using the same, high flowability and high mechanical properties can be both achieved, variability in the mechanical properties is small, and the carbon fiber followability to a small portion is also excellent.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram showing an example of a carding machine.

FIG. 2 is a schematic diagram showing an example of an air laid machine.

FIGS. 3(A) and 3(B) are schematic diagrams of a measurement device showing a determination method of a drape value.

EXPLANATION OF SYMBOLS

-   -   1: carding machine     -   2: cylinder roll     -   3: take-in roll     -   4: doffer roll     -   5: worker roll     -   6: stripper roll     -   7: feed roll     -   8: belt conveyer     -   9: discontinuous carbon fibers     -   10: sheet-like web     -   11: air laid machine     -   12: drum     -   13: pin cylinder     -   14: wire     -   15: suction box     -   21: carbon fiber bundle     -   22: fixing tape     -   23: weight     -   24: table     -   25: carbon fiber bundle     -   26: fixing tape

DETAILED DESCRIPTION

Hereinafter, our fabrics will be explained in detail together with Examples and Comparative Examples.

First, although the carbon fibers are not particularly restricted, high-strength and high-elastic modulus carbon fibers can be used, and one kind of carbon fibers may be used or two or more kinds of carbon fibers may be used together. In particular, PAN-based, pitch-based and rayon-based carbon fibers can be exemplified. From the viewpoint of the balance between the strength and the elastic modulus of a molded article to be obtained, PAN-based carbon fibers are more preferable. The density of carbon fibers is preferably 1.65 to 1.95 g/cm³, and more preferably 1.70 to 1.85 g/cm³. If the density is too high, lightness in weight of a carbon fiber-reinforced plastic obtained is poor and, if too low, the mechanical properties of a carbon fiber-reinforced plastic obtained become low.

Further, the carbon fibers are preferably formed as a bundle from the viewpoint of productivity, and it is preferred that the number of single fibers in the bundle is many. The number of single fibers for the carbon fiber bundle can be 1,000 to 350,000 and, in particular, 10,000 to 100,000.

The single fiber flexural stiffness of carbon fibers is preferably 1.0×10⁻¹¹ to 2.8×10⁻¹¹ (Pa·cm⁴), and more preferably 1.0×10⁻¹¹ to 1.5×10⁻¹¹ (Pa·cm⁴). By the condition where the single fiber flexural stiffness is in the above-described range, in the process of manufacturing a carbon fiber nonwoven fabric described later, it makes possible to stabilize the quality of carbon fiber nonwoven fabric obtained.

For the purpose of improving the adhesive property between carbon fibers and a matrix resin when a carbon fiber composite material is molded, it is preferred that the carbon fibers are surface treated. As the method of the surface treatment, there are electrolytic treatment, ozone treatment, ultraviolet treatment or the like.

Then, in a carbon fiber nonwoven fabric according to the first example, the carbon fibers are sized with an aliphatic compound having a plurality of epoxy groups. The aliphatic compound means a noncyclic straight-chain saturated hydrocarbon, a branched-chain saturated hydrocarbon, a noncyclic straight-chain unsaturated hydrocarbon, a branched-chain unsaturated hydrocarbon, or a chain-structure compound substituting oxygen atom (O), nitrogen atom (NH, N), sulfur atom (SO₃H, SH) or carbonyl atomic group (CO) for the carbon atom of the above-described hydrocarbons (CH₃, CH₂, CH, C).

Further, it is preferred that the above-described compound having a plurality of epoxy groups is a compound having an epoxy group at each end of the longest atomic chain, in particular, a compound having an epoxy group only at each end of the longest atomic chain. In a compound having a plurality of epoxy groups, an atomic chain having the greatest total number of atoms among the total numbers of carbon atoms and heteroatoms (oxygen atom, nitrogen atom and the like) forming respective chain structures which link between two epoxy groups is defined as the longest atomic chain, and the total number of atoms forming the longest atomic chain is defined as a number of atoms of the longest atomic chain. The number of atoms such as hydrogen linked to the atoms forming the longest atomic chain is not included to the total number.

Although the structure of a side chain is not particularly restricted, a structure hard to become a crosslinking point is preferred to prevent that a density of crosslinking between molecules of a compound of a sizing agent becomes too great.

If the number of epoxy groups in a compound of a sizing agent is less than 2, it cannot be done to effectively bridge between carbon fibers and a matrix resin. Therefore, the number of epoxy groups is necessary to be two or more to effectively bridge between carbon fibers and a matrix resin.

On the other hand, if the number of epoxy groups is too large, because the density of crosslinking between molecules of a compound of a sizing agent becomes great and it causes a brittle sizing layer and as a result a tensile strength of a composite is reduced, the number of epoxy groups is preferably 6 or less, more preferably 4 or less, and further preferably, it is 2. Furthermore, it is more preferred that these two epoxy groups are present at both ends of the longest atomic chain. Namely, by the presence of the epoxy groups at both ends of the longest atomic chain because it is prevented that a local density of crosslinking increases, such a structure is preferred for a tensile strength of a composite.

As a structure of the epoxy group, a glycidyl group having a high reactivity is preferred.

The molecular weight of such an aliphatic compound is preferably 80 or more and 3,200 or less, more preferably 100 or more and 1,500 or less, and further preferably 200 or more and 1,000 or less, from the viewpoint of preventing deterioration of handling ability as a sizing agent caused by a condition that the resin viscosity is too low or too high.

As concrete examples of the aliphatic compound having a plurality of epoxy groups, for example, as diglycidyl ether compounds, can be exemplified ethylene glycol diglycidyl ether and polyethylene glycol diglycidyl ether group, propylene glycol diglycidyl ether and polypropylene glycol diglycidyl ether group, 1,4-butanediol diglycidyl ether, neopentyl glycol diglycidyl ether, polytetramethylene glycol diglycidyl ether, polyalkylene glycol diglycidyl ether group or the like. Further, as polyglycidyl ether compounds, can be exemplified glycerol polyglycidyl ether, diglycerol polyglycidyl ether, polyglycerol polyglycidyl ether group, sorbitol polyglycidyl ether group, arabitol polyglycidyl ether group, trimethylol propane polyglycidyl ether group, pentaerythritol polyglycidyl ether group, polyglycidyl ether group of aliphatic polyatomic alcohol or the like.

Preferably, it is a polyglycidyl ether compound having a glycidyl group high in reactivity. Further preferably, polyethylene glycol diglycidyl ether group, polypropylene glycol diglycidyl ether group, alkane diol diglycidyl ether group, and compounds having the following structures are preferred:

wherein G represents a glycidyl group, R¹ represents —CH₂CH₂—, —CH₂CH₂CH₂— or —CH(CH₃) CH₂—, R² represents —CH₂—, at least two of R³, R⁴ and R⁵ represent -G and the other represents —H or -G, m represents an integer of 1 to 25, n represents an integer of 2 to 75, x, y and z represent zero or a positive integer, and x+y+z is preferably 0 to 25. Further, a mixture of these compounds may be used.

In the aliphatic compound having a plurality of epoxy groups, it is preferred that the number of atoms of the longest atomic chain is 20 or more. Namely, if the number of atoms is less than 20, there is a possibility that the density of crosslinking in the sizing layer becomes high and therefore it is likely to become a structure low in toughness, and as a result, a tensile strength of a composite is hard to be exhibited. To the contrary, if the number of atoms of the longest atomic chain is greater, because the sizing layer is flexible and is likely to become a structure high in toughness, as a result, a tensile strength of a composite is liable to be increased and, in particular, because there is a feature that a tensile strength in a brittle resin is high, more preferably, the number of atoms of the longest atomic chain is 25 or more, and further preferably, 30 or more.

However, the greater the number of atoms of the longest atomic chain is, more flexible the structure becomes, but if too long, there is a possibility that the chain is bent and a functional group is sequestered and as a result, the adhesive property between carbon fibers and a resin is reduced, the number of atoms is preferably 200 or less, more preferably 100 or less.

When the aliphatic compound contains a cyclic aliphatic skeletal structure, if the epoxy group is sufficiently apart from the cyclic skeletal structure, concretely, if apart from by 6 or more in number of atoms, it can be used.

In a carbon fiber nonwoven fabric according to the second example, an aromatic compound having a plurality of epoxy groups in which a number of atoms present between an epoxy group and an aromatic ring is 6 or more is used as the sizing agent. The “number of atoms present between an epoxy group and an aromatic ring” means the total number of carbon atoms, heteroatoms (oxygen atom, nitrogen atom and the like) and carbonyl atomic groups forming chain structures which link between the epoxy group and the aromatic ring.

If the number of atoms present between an epoxy group and an aromatic ring is less than 6 as the sizing agent, because a rigid and three-dimensionally large compound is interposed at an interface between carbon fibers and a matrix resin, the reactivity with a surface functional group present on the outermost surfaces of carbon fibers is not improved, and as a result, improvement of the properties in the lateral direction of a composite material cannot be expected.

Concretely, a compound shown in formula (9) can be exemplified:

wherein R¹ in the formula (9) represents chemical formula (10):

R² represents an alkylene group having a carbon number of 2 to 30, R³ is —H or —CH₃, m and n represent an integer of 2 to 48, and m+n is 4 to 50.

In this case, it is preferred the molecular chain of the compound is straight chain like having a flexibility and the molecular weight thereof is small to not interpose a rigid and three-dimensionally large compound at an interface between carbon fibers and a matrix resin in a carbon fiber composite material and, therefore, each of the above-described m, n is 2 or more, preferably 3 or more, further preferably 5 or more, and the above-described m+n is 4 or more, preferably 6 or more, further preferably 10 or more. In a compound in which each of m, n is less than 2 or m+n is less than 4, there is a possibility that the adhesive property between a matrix resin and carbon fibers is reduced. On the other hand, if m+n exceeds 50, there is a possibility that the compatibility with a matrix resin is reduced and the adhesive property between a matrix resin and carbon fibers is reduced. Further, in the formula (9), it is preferred that R² is —CH₂CH₂— or CH(CH₃)CH₂—.

The bisphenol A part or B part has an advantage of improving the compatibility with a matrix resin and an advantage of improving the fluff resistance.

In the above description, the skeletal structure of the aromatic compound having a plurality of epoxy groups in which a number of atoms present between an epoxy group and an aromatic ring is 6 or more may also be a condensed polycyclic aromatic compound. As the skeletal structure of the condensed polycyclic aromatic compound, for example, naphthalene, anthracene, phenanthrene, chrysene, pyrene, naphthacene, triphenylene, 1,2-benzanthracene, benzopyrene or the like can be exemplified. Desirably, naphthalene, anthracene, phenanthrene and pyrene, whose skeletal structures are small, are preferred.

The epoxy equivalent of the condensed polycyclic aromatic compound having a plurality of epoxy groups is preferably 150 to 350, more preferably 200 to 300, from the viewpoint of obtaining an advantage of improving the adhesive property sufficiently.

The molecular weight of the condensed polycyclic aromatic compound having a plurality of epoxy groups is preferably 400 to 800, more preferably 400 to 600, from the viewpoint of preventing deterioration of handling ability as a sizing agent caused by increase of the resin viscosity.

Further, to the above-described sizing agent, the other components such as a bisphenol-type epoxy compound having a small molecular weight such as “Epikote” 828 or “Epikote” 834, a straight-chain like low molecular weight epoxy compound, polyethylene glycol, polyurethane, a polyester, an emulsifier or a surfactant, may be added, for the purpose of adjustment of viscosity, improvement of abrasion resistance, improvement of fluff resistance, improvement of convergence of fibers, improvement of higher-order processability or the like.

Furthermore, there is no problem even in adding a rubber such as nitrile-butadiene rubber, a straight-chain like epoxy modified compound having an elastomer property such as epoxy end group nitrile-butadiene rubber or the like.

The adhesion amount of the sizing agent to carbon fibers is preferably 0.01 wt. % or more and 10 wt. % or less per unit weight of carbon fibers, more preferably 0.05 wt. % or more and 5 wt. % or less, further preferably 0.1 wt. % or more and 2 wt. % or less, from the viewpoint of making the width of improvement of adhesive property with a resin while preventing the sizing agent from being consumed excessively.

It is preferred that the sizing agent is uniformly coated. Namely, it is preferred that the thickness of the sizing agent layer is 20 to 200 angstroms and the maximum value of the thickness does not exceed two times of the minimum value. By such a uniform sizing agent layer, a coupling effect can be exhibited more effectively.

In a carbon fiber nonwoven fabric according to the third example, at least one kind of a specified compound selected from the aforementioned chemical formulae (3), (4) and (5) (hereinafter, also referred to as merely “a sizing agent”) is made adhere to the carbon fibers of the carbon fiber nonwoven fabric at an amount of 0.1 to 5.0 wt. % relative to the weight of the carbon fibers of 100 wt. %. Polyethylene oxide part or polypropylene oxide part in such a compound gives a smoothness to carbon fibers, exhibits an effect of reducing a friction force, and when formed to a carbon fiber nonwoven fabric described later, a friction force caused by tangle of carbon fibers to each other can be reduced, thereby improving flowability and the formability. On the other hand, bisphenol A part has an effect of improving the compatibility with a matrix resin. By using the above-described respective components at a condition being copolymerized, the compatibility with a resin can be maintained as compared to when the respective single components are used at a condition being mixed, and the effect of greatly reducing a coefficient of friction.

Further, in the above-described sizing agent, in a compound in which m+n in the aforementioned chemical formula is less than 10, an effect of reducing a coefficient of friction is poor, and such a compound is not preferred. Further, if m+n exceeds 50, because the compatibility with a matrix resin is reduced and the adhesive property between the matrix resin and carbon fibers is reduced, such a compound is not preferred.

As the treatment using such a sizing agent, generally a treatment method can be employed wherein a liquid containing a sizing agent (sizing liquid) is made adhere after water wet carbon fiber bundles having a moisture content of approximately 20 to 80 wt. %, wetted with water in known surface treatment process and water washing process, are dried.

Although the method of providing a sizing agent is not particularly limited, for example, there are a method of dipping carbon fibers in a sizing liquid via rollers, a method of bringing carbon fibers into contact with rollers adhered with a sizing liquid, a method of spraying an atomized sizing liquid and the like. Further, although the method may be any of batch type and continuous type, continuous type good in productivity and small in unevenness is preferred. In this connection, it is preferred to control the concentration and temperature of the sizing liquid, yarn tension and the like, so that the adhesion amount of sizing agent effective component relative to carbon fibers becomes uniform. Further, it is more preferred to vibrate carbon fibers with a ultrasonic wave when the sizing agent is provided.

Although the drying temperature and the drying time should be adjusted depending upon the adhesion amount of the compound, the drying temperature is preferably 130° C. or higher and 350° C. or lower, and more preferably 180° C. or higher and 250° C. or lower, from the viewpoints of completely removing a solvent used for providing the sizing agent, shortening the time required for drying, on the other hand, preventing thermal deterioration of the sizing agent and preventing deterioration of the spreading property of carbon fiber bundles caused by the bundles being hardened.

As the solvent used for the sizing agent, although water, methanol, ethanol, dimethyl formamide, dimethyl acetamide, acetone and the like can be exemplified, water is preferred from the viewpoints of easy handling ability and disaster prevention. Therefore, when a compound insoluble or slightly soluble in water is used as a sizing agent, it is preferred to use it after making it water dispersible by adding an emulsifier, a surfactant and the like. Concretely, as the emulsifier or the surfactant, can be used anionic emulsifiers such as styrene-maleic anhydride copolymer, olefin-maleic anhydride copolymer, formalin condensate of naphthalene sulfonate and polyacrylic soda, cationic emulsifiers such as polyethylene imine and polyvinyl imidazoline, nonionic emulsifiers such as nonyl phenol ethylene oxide adduct, polyvinyl alcohol, copolymer of polyoxyethylene ether ester and sorbitan ester ethyl oxide adduct, and nonionic emulsifiers small in interaction with epoxy groups are preferred.

The adhesion amount of a sizing agent relative to the mass of only the carbon fibers is preferably 0.01 mass % or more and 10 mass % or less, more preferably 0.05 mass % or more and 5 mass % or less, and further preferably 0.1 mass % or more and 2 mass % or less. If less than 0.01 mass %, the effect of improving the adhesive property is hardly exhibited. If more than 10 mass %, there is a possibility that the mechanical properties when the carbon fiber nonwoven fabric is made into a molded article of a carbon fiber composite material may be reduced.

For the carbon fiber bundles, to obtain the carbon fiber aggregates described later, the drape value/single fiber flexural stiffness, determined by dividing the drape value, that is an index representing the hardness of the carbon fiber bundle, with the single fiber flexural stiffness, is preferably 1.4×10³ to 4.0×10³ cm/(Pa·cm⁴), and more preferably 1.5×10³ to 3.0×10³ cm/(Pa·cm⁴). If the drape value/single fiber flexural stiffness is less than 1.4×10³ cm/(Pa·cm⁴), the convergence of the fibers is poor, in the process of preparing the carbon fiber aggregates such as air laid or carding described later, the fibers are liable to be spread, there is a possibility that the moldability deteriorates when made into a carbon fiber composite material, and if it exceeds 4.0×10³ cm/(Pa·cm⁴), there is a possibility that the wettability with a matrix resin deteriorates and the mechanical properties are reduced when made into a carbon fiber composite material.

As the process of obtaining carbon fiber aggregates, a process such as carding or air laid can be exemplified. Carding means an operation of arranging the direction of discontinuous fibers or spreading fibers by applying a force in an approximately same direction to the aggregates of discontinuous fibers with a comb-like member. Generally, it is performed using a carding machine equipped with a roll having many needle-like projections on the surface and/or a roll wound with a metallic wire having saw blade-like projections.

When such a carding is carried out, it is preferred to control the time (residing time), during which carbon fibers reside in the carding machine, to be short, for the purpose of preventing the carbon fibers from being folded. Concretely, it is preferred to transfer the carbon fibers existing on the wires wound onto a cylinder roll of the carding machine to a doffer roll in a time as short as possible. Therefore, to accelerate such a transfer, it is preferred to rotate the cylinder roll at a high rotational speed, for example, such as 150 rpm or higher. Further, from a similar reason, the surface speed of the doffer roll is preferably a high speed, for example, such as 10 m/min. or higher.

The process of carding the carbon fiber bundles is not particularly restricted, and a general one can be used. For example, as shown in FIG. 1, a carding machine 1 mainly comprises a cylinder roll 2, a take-in roll 3 provided at an upstream side and closely to the outer circumferential surface of the cylinder roll 2, a doffer roll 4 provided closely to the outer circumferential surface of the cylinder roll 2 at a downstream side which is a side opposite to the side of the take-in roll 3, a plurality of worker rolls 5 provided closely to the outer circumferential surface of the cylinder roll 2 between the take-in roll 3 and the doffer roll 4, stripper rolls 6 provided closely to the worker rolls 5, and a feed roll 7 provided closely to the take-in roll 3, and a belt conveyer 8.

Discontinuous carbon fiber bundles 9 are supplied to belt conveyer 8, and the carbon fiber bundles 9 are introduced onto the outer circumferential surface of cylinder roll 2 through the outer circumferential surface of feed roll 7 and then through the outer circumferential surface of take-in roll 3. Up to this stage, the carbon fiber bundles are spread and become floc-like aggregates of carbon fiber bundles. Although a part of the floc-like aggregates of carbon fiber bundles introduced onto the outer circumferential surface of cylinder roll 2 wind around the outer circumferential surfaces of worker rolls 5, these carbon fibers are stripped off by stripper rolls 6 and returned again onto the outer circumferential surface of the cylinder roll 2. Many needles, projections exist at standing conditions on the outer circumferential surfaces of the respective rolls of feed roll 7, take-in roll 3, cylinder roll 2, worker rolls 5 and stripper rolls 6, and in the above-described steps, by the operation of the needles, the carbon fiber bundles are spread into predetermined-condition bundles, and oriented to some extent. The carbon fiber bundles, spread into predetermined-condition bundles through such steps, move onto the outer circumferential surface of doffer roll 4 as a sheet-like web 10 which is one form of the carbon fiber aggregates.

Air laid is a process of producing a nonwoven fabric sheet of short fibers, it is not particularly restricted, and a general one can be used. As general air laid processes, can be exemplified Honshu Paper process, Kroyer process, Danweb process, J&J process, KC process, Scott process or the like.

For example, as shown in FIG. 2, air laid machine 11 has drums 12 rotated in directions reverse to each other, each formed in a cylinder shape and having small holes, and pin cylinders 13 provided in the respective drums 12. Carbon fiber bundle single materials or carbon fiber bundles and thermoplastic resin fibers are air transported to drums 12 together with a large amount of air, they are spread by pin cylinders 13 in drums 12, discharged from the small holes, and they drop onto wires 14 running thereunder. The air used for air transportation is sucked into a suction box 15 provided under wires 14, and only spread carbon fiber bundle single materials or spread carbon fiber bundles and thermoplastic resin fibers are left on wires 14 to form a carbon fiber nonwoven fabric.

Further, the carbon fiber nonwoven fabric indicated here means a fabric which is kept in form by tangle or friction of fibers to each other at a condition where discontinuous carbon fiber bundles are spread and oriented by the above-described carding or air laid, and can be exemplified a thin sheet-like web, a nonwoven fabric obtained by laminating webs, as needed, by tangle or adhesion or the like. From the viewpoint of preventing carbon fibers from being folded or bent and suppressing the tangle force pf fibers to each other to achieve a good flowability when made into a carbon fiber composite material, the carbon fiber nonwoven fabric is obtained preferably by air laid, and from the viewpoint of uniformity of nonwoven fabric, it is obtained preferably by carding.

Although the carbon fiber nonwoven fabric may be formed by only carbon fibers, thermoplastic resin fibers and/or thermoplastic resin particles can also be contained. It is preferred to add thermoplastic resin fibers because breakage of carbon fibers at the process of air laid or carding can be prevented. Because carbon fibers are rigid and fragile, they are hard to be tangled and liable to be broken. Therefore, there is a problem in the carbon fiber nonwoven fabric formed by only carbon fibers that during the production, the fabric is easily cut or the carbon fibers are liable to be fallen off. In the air laid process, by containing thermoplastic resin fibers and/or thermoplastic resin particles, the handling ability of the carbon fiber nonwoven fabric can be improved by carrying out a method of thermally fusing them by pressing or heat treatment due to thermal calender rollers or thermal emboss rollers or a method of tangling the fibers by needle punch or water jet needle or the like, employed at a later step. In the carding process, by containing thermoplastic resin fibers which are flexible and hard to be broken and liable to be tangled, carbon fiber aggregates high in uniformity can be formed. When thermoplastic resin fibers are contained in carbon fiber aggregates, the content of carbon fibers in the carbon fiber aggregates is preferably 20 to 95 mass %, more preferably 50 to 95 mass %, and further preferably 70 to 95 mass %. If the rate of carbon fibers is low, it becomes difficult to obtain high mechanical properties when made into a carbon fiber composite material, and to the contrary, if the rate of thermoplastic resin fibers is too low, the above-described advantage of improving uniformity of the carbon fiber aggregates cannot be obtained.

As to the carbon fiber bundles in the carbon fiber nonwoven fabric, a number average x of carbon fibers forming a carbon fiber bundle (1), in which a number of carbon fibers forming a carbon fiber bundle is 90 or more, is 90 to 1,000. From the viewpoint of improving the carbon fiber strength utilization factor and the surface appearance of a molded article when made into a carbon fiber composite material described later, the number average x of carbon fibers forming the bundle is preferably 90 to 600, more preferably 90 to 500. From the viewpoint of increasing the content of carbon fibers when made into a carbon fiber composite material and obtaining a high elastic modulus, the number average x is preferably 300 to 1,000, more preferably 500 to 1,000. If the number average x of carbon fibers of the carbon fiber bundles is less than 90, the number of tangles of fibers to each other increases, and flowability deteriorates. If more than 1,000, the mechanical properties and followability of carbon fibers to small parts deteriorate, and the variability in mechanical properties becomes great.

As to the carbon fiber bundles in the carbon fiber nonwoven fabric, it is preferred that a proportion of the carbon fiber bundles (1), in which the number of carbon fibers forming a carbon fiber bundle is 90 or more, relative to the total weight of carbon fibers in the carbon fiber nonwoven fabric is 5 wt. % or more and 80 wt. % or less. From the viewpoint of improving the carbon fiber strength utilization factor and the surface appearance of a molded article, it is preferably 5 wt. % or more and 50 wt. % or less, further preferably 5 wt. % or more and 45 wt. % or less. From the viewpoints of further improving flowability, increasing the content of carbon fibers when made into a carbon fiber composite material and obtaining a high elastic modulus, it is preferably more than 30 wt. % and 80 wt. % or less, further preferably more than 35 wt. % and 80 wt. % or less. From the viewpoint of balance of carbon fiber strength utilization factor, surface appearance of a molded article and flowability, it is preferably more than 30 wt. % and 50 wt. % or less. If the proportion of the carbon fiber bundles (1) is less than 5 wt. %, the number of tangles of fibers to each other increases, and flowability deteriorates. If more than 80 wt. %, the mechanical properties and followability of carbon fibers to small parts deteriorate, and variability in mechanical properties becomes great.

By the condition where a standard deviation σ of the number x_(n) of carbon fibers forming the above-described carbon fiber bundle (1) in the carbon fiber nonwoven fabric satisfies 50≦σ≦500 and the carbon fiber bundles are distributed in the carbon fiber nonwoven fabric by being dispersed, a carbon fiber nonwoven fabric can be obtained in which high flowability and mechanical properties can be both satisfied, the variability in mechanical properties is small, and which is excellent also in followability of carbon fibers to small parts. If the above-described standard deviation σ is less than 50, flowability deteriorates, and if the above-described standard deviation σ is more than 500, the mechanical properties deteriorate and variability in mechanical properties becomes great. The above-described standard deviation σ is preferably 100≦σ≦350, more preferably 150≦σ≦350, and further preferably 150≦σ≦300.

When thermoplastic resin fibers are contained in the carbon fiber aggregates, the fiber length of the thermoplastic resin fibers is not particularly limited as long as it is capable of achieving keeping the form of the carbon fiber aggregate or preventing falling off of carbon fibers and, generally, thermoplastic resin fibers having a length of approximately 3 to 100 mm can be used. It is also possible to decide the fiber length of thermoplastic resin fibers relatively in accordance with the fiber length of carbon fibers.

Further, in the above-described carding, it is preferred to provide a crimp to the thermoplastic resin fibers for the purpose of enhancing the effect of tangle due to the thermoplastic resin fibers. The degree of the crimp is not particularly limited as long as it is capable of achieving thermoplastic resin fibers having a number of crimps of approximately 5 to 25 crests per 25 mm and a rate of crimp of approximately 3 to 30% can be used.

When thermoplastic resin particles are contained in the carbon fiber aggregates, as the shape of the thermoplastic resin particles, a spherical shape, a small piece-like shape, and columnar shape such as a pellet, can be exemplified. In a spherical shape, the preferable average particle diameter is 0.01 to 1,000 μm.

The material for the above-described thermoplastic resin fibers is not particularly restricted, and it can be appropriately selected from a range that does not greatly reduce the mechanical properties of a carbon fiber composite material. For example, fibers can be used which are prepared by spinning a resin such as a polyolefin-group resin such as polyethylene or polypropylene, a polyamide-group resin such as nylon 6 or nylon 6,6, a polyester-group resin such as polyethylene terephthalate or polybutylene terephthalate, a polyetherketone, a polyethersulfone or an aromatic polyamide. It is preferred that such a material for thermoplastic resin fibers is appropriately selected in accordance with the combination with a matrix resin. In particular, thermoplastic resin fibers prepared using the same resin as a matrix resin, a resin having a compatibility with a matrix resin or a resin having a high adhesive property with a matrix resin is preferred, because the mechanical properties of a carbon fiber-reinforced plastic are not lowered. For example, the thermoplastic resin fibers are preferred to be composed of at least one kind of fibers selected from the group consisting of polyamide fibers, polyphenylene sulfide fibers, polypropylene fibers, polyetheretherketone fibers and phenoxy resin fibers.

When a matrix resin is impregnated into the carbon fiber nonwoven fabric, a method may be employed wherein carbon fiber nonwoven fabric containing thermoplastic resin fibers is prepared and the thermoplastic resin fibers contained in the carbon fiber nonwoven fabric are used as the matrix resin as they are, or a method may also be employed wherein carbon fiber nonwoven fabric not containing thermoplastic resin fibers is used as a raw material, and a matrix resin is impregnated at an arbitrary stage for producing a carbon fiber composite material. Further, even when the carbon fiber nonwoven fabric containing thermoplastic resin fibers is used as the raw material, a matrix resin can be impregnated at an arbitrary stage for producing a carbon fiber composite material. In such a case, a resin forming thermoplastic resin fibers and a matrix resin may be an identical resin, or may be resins different from each other. When the resin forming thermoplastic resin fibers and the matrix resin are different from each other, it is preferred that both resins have a compatibility or a high affinity.

When the carbon fiber composite material is produced, a thermoplastic resin as a matrix resin is impregnated into the above-described carbon fiber nonwoven fabric, and the impregnation step for manufacturing the carbon fiber composite material can be carried out using a press machine having a heating function. The press machine is not particularly restricted as long as it can realize temperature and pressure required for impregnation of the matrix resin, a usual press machine having a plane-like platen moved vertically, or a so-called “double belt” press machine having a mechanism that runs a pair of endless steel belts can be used. In such an impregnation step, after the matrix resin is prepared in a sheet-like form such as a film, a nonwoven fabric or a woven fabric, it is laminated with the carbon fiber nonwoven fabric, and at that condition, the matrix resin can be melted and impregnated using the above-described press machine and the like. Further, a method can also be employed wherein discontinuous fibers are prepared using a matrix resin, by mixing them and inorganic fibers at a step of making a carbon fiber nonwoven fabric, a carbon fiber nonwoven fabric containing the matrix resin and the inorganic fibers is prepared, and this carbon fiber nonwoven fabric is heated and pressed using the press machine and the like.

Next, Examples and Comparative Examples will be explained.

First, the properties and determination methods used in the Examples and Comparative Examples will be explained.

(1) Method of Determining Fiber Bundles:

A sample with a size of 100 mm×100 mm was cut out from a carbon fiber nonwoven fabric and, thereafter, the sample was heated in an electric furnace heated at 500° C. for about one hour to burn off organic substances such as thermoplastic resin fibers. After the mass of carbon fiber nonwoven fabric left after being cooled down to a room temperature was determined, carbon fiber bundles were all extracted from the carbon fiber nonwoven fabric by a pincette. With respect to all the extracted carbon fiber bundles, using a balance capable of measuring up to a degree of 1/10,000g, the weight Mn and the length Ln of each carbon fiber bundle is determined. After the determination, for each bundle, the number of single fibers of carbon fibers forming the carbon fiber bundle x_(n)=Mn/(Ln×F) is calculated. F is a fineness of carbon fibers, and x_(n) is a number of single fibers forming the carbon fiber bundle. The determination is carried out at a condition where carbon fiber bundles, in each of which the number of single fibers of carbon fibers forming the carbon fiber bundle x_(n) is 90 or more, are referred to as carbon fiber bundles (1), the total weight is referred to as M₁ and the total number of bundles is referred to as N. Further, the determination is carried out at a condition where carbon fiber bundles, in each of which the number of single fibers of carbon fibers forming the bundle is less than 90, are referred to as fiber bundles (2), and the total weight of the carbon fiber bundles (2) is referred to as M₂. For fiber bundles spread to a degree at which the bundles cannot be extracted by a pincette, the weight thereof was determined in the lump at the last. Further, when the fiber length is small and determination of weight becomes difficult, the fiber lengths may be classified at an interval of about 0.2 mm and the weights of a plurality of classified bundles may be determined in the lump, and an average value thereof may be used. After classifying and determining all bundles, a number average x of carbon fibers forming the carbon fiber bundle (1)=Σ{Mn/(Ln×F)}/N and a standard deviation σ of the number x_(n) of carbon fibers forming the carbon fiber bundle={1/N×Σ(x_(n)−x)²}^(1/2) are calculated, and the average value X of Mn/Ln of carbon fiber bundles (1), the number average x of carbon fibers forming the bundle and the standard deviation σ of the number x_(n) of carbon fibers forming the carbon fiber bundle are determined. N is the total number of bundles of the carbon fiber bundles (1). Further, the proportion of carbon fiber bundles (1) relative to the total weight of carbon fiber bundles is determined by the following equation:

M ₁/(M ₁ +M ₂)×100.

(2) Flow Test (Stamping Molding):

After two sheets of carbon fiber composite materials each having a size of 100 mm×100 mm×2 mm were preheated at a temperature of a melting point of a thermoplastic resin+40° C. (for example, 260° C. in nylon 6), two sheets were stacked and placed on a press table heated at 120° C., and pressed at 20 MPa for 5 seconds. The area of the sheet after this pressing A2 and the area before the pressing A1 were measured, and A2/A1 was determined as flowability (%).

(3) Vf (Content of Carbon Fibers in Carbon Fiber Composite Material):

A sample of about 2 g was cut out from a molded article of a carbon fiber composite material, and the mass thereof was determined. Thereafter, the sample was heated in an electric furnace heated at 500° C. for one hour and organic substances such as a matrix resin were burnt off. After being cooled down to a room temperature, the mass of the residual carbon fibers was determined. The rate of the mass of the carbon fibers to the mass of the sample before being burnt off with organic substances such as a matrix resin was determined, and it was defined as the content of carbon fibers.

(4) Flexural Test:

A flexural strength was determined based on JIS-K7171.

(5) Fiber Strength Utilization Factor:

It was calculated by the following equation:

Fiber strength utilization factor=Flexural strength/Vf

(6) Single Fiber Flexural Stiffness (Pa·m⁴):

It was calculated by Single fiber flexural stiffness=E×I.

E: single fiber elastic modulus, and

I: geometrical moment of inertia.

The cross section of a fiber was supposed as a true circle, the geometrical moment of inertia was determined from the fiber diameter D, and the flexural stiffness was determined from the single fiber tensile elastic modulus and the geometrical moment of inertia.

(7) Drape Value/Single Fiber Flexural Stiffness:

It was determined as an index of the convergence of a sizing agent (Sz agent) by dividing the drape value, that is an index representing the hardness of the carbon fiber bundle, with the single fiber flexural stiffness.

(8) Drape Value (cm) of Carbon Fiber Bundle:

As shown in FIG. 3(A), a carbon fiber bundle 21 drawn out from a bobbin without applying a tension is cut at a length of 40 cm, one end thereof is fixed by a fixing tape 22, a weight 23 of 100 g is hung at the other end thereof, and after the twist and the bending are corrected, it is left in a measurement-temperature atmosphere for 30 minutes. Next, the weight 23 is removed, as shown in FIG. 3(B), the carbon fiber bundle 25 is placed on a horizontal and rectangular table 24 having a corner of 90° to protrude from the table by 25 cm, and after the part of carbon fibers on the table is fixed by a fixing tape 26 while the carbon fiber bundle with 40 cm is supported to not be broken, the support for the part protruding from the table is removed and the part is hung down, and after 2 seconds, the length of a horizontal distance L from the beginning point is measured, and the average value of “n” number of 3 times is defined as a drape value.

(9) Coefficient of Friction:

A friction device was used wherein 5 stainless rods each having a diameter of 10 mm (chrome plating, surface roughness: 1 to 1.5 s) were arranged in parallel to each other at an interval of 50 mm at a zigzag arrangement style so that a carbon fiber yarn could pass through the surfaces of the rods with a contact angle of 120° per each rod surface. The carbon fiber yarn was passed through this device at a yarn speed of 3 m/min. and an inlet side tension of 0.09 g per 1 denier, and the coefficient of friction was determined from the rate of the inlet side tension and an outlet side tension by the following equation:

Coefficient of friction=(3/8π)ln(T ₂ /T ₁)

T₁: inlet side yarn tension

T₂: outlet side yarn tension

EXAMPLES

First, carbon fiber bundles and sizing agents used in Examples 1 to 7 and Comparative Examples 1 to 3 will be explained.

Carbon Fiber Bundle (A):

To a continuous carbon fiber bundle having a fiber diameter of 7 μm, a tensile elastic modulus of 230 GPa, a single fiber flexural stiffness of 2.71×10⁻¹¹ Pa·m⁴ and a number of filaments of 24,000, a sizing agent, prepared by preparing a mother liquor of the sizing agent by diluting glycerol triglycidyl ether with dimethyl formamide (hereinafter, abbreviated as DMF) so that the resin component became 1 wt. %, was provided to the carbon fibers by dipping method, and drying was carried out at 230° C. The adhesion amount was 0.4 wt. %.

Carbon Fiber Bundle (B):

The carbon fiber bundle was prepared in a manner similar to that in the carbon fiber bundle (A) other than a condition where the sizing agent was changed to glycerol diglycidyl ether.

Carbon Fiber Bundle (C):

The carbon fiber bundle was prepared in a manner similar to that in the carbon fiber bundle (A) other than a condition where the sizing agent was changed to polyethylene glycol diglycidyl ether (in the chemical formula (1), R¹ is —CH₂CH₂— and m=9).

Carbon Fiber Bundle (D):

The carbon fiber bundle was prepared in a manner similar to that in the carbon fiber bundle (A) other than a condition where the sizing agent was changed to diglycerol polyglycidyl ether.

Carbon Fiber Bundle (E):

The carbon fiber bundle was prepared in a manner similar to that in the carbon fiber bundle (A) other than a condition where the sizing agent was changed to diethylene glycol diglycidyl ether.

Carbon Fiber Bundle (F):

The carbon fiber bundle was prepared in a manner similar to that in the carbon fiber bundle (A) other than a condition where the sizing agent was changed to bisphenol A type diglycidyl ether having an aromatic ring; “Epikote” 828 (epoxy compound having an aromatic ring) supplied by Yuka Shell Epoxy Kabushiki Kaisha.

Carbon Fiber Bundle (G):

The carbon fiber bundle was prepared in a manner similar to that in the carbon fiber bundle (A) other than a condition where the sizing agent was changed to phenol novolak type glycidyl ether; “Epikote” 154 (epoxy compound having an aromatic ring) supplied by Yuka Shell Epoxy Kabushiki Kaisha.

Example 1

The carbon fiber bundle (A) was cut at a fiber length of 15 mm, the cut carbon fiber bundles (A) and nylon 6 short fibers (fineness of short fiber: 1.7 dtex, cut length: 51 mm, number of crimps: 12 crests per 25 mm, rate of crimp: 15%) were mixed at a mass ratio of 90:10, and the mixture was introduced into a carding machine. The web having come out was cross wrapped to form a sheet-like carbon fiber nonwoven fabric comprising carbon fiber bundles (A) and nylon 6 fibers and having an areal weight of 100 g/cm². The proportion of the carbon fiber bundles (1) relative to the total weight of carbon fibers in the carbon fiber nonwoven fabric was 18 wt. %, the number average x of carbon fibers forming the bundle was 160, and the standard deviation σ was 70.

The winding direction of the sheet-like carbon fiber nonwoven fabric was referred to as 0°, the sheets of the carbon fiber nonwoven fabrics were stacked at 0°/90° and, further, after a nylon resin film (“CM1001”, ηr=2.3, supplied by Toray Industries, Inc.) was stacked so that the volume ratio of the carbon fibers to the thermoplastic resin became 30:70 as the whole of the stacked carbon fiber nonwoven fabrics, the whole was nipped by stainless plates, and after preheating at 260° C. for 90 seconds, it was hot pressed at 260° C. for 180 seconds while being applied with a pressure of 2.0 MPa. Then, it was cooled down to 50° C. at the pressed condition to obtain a flat plate of carbon fiber composite material having a thickness of 2 mm. When the flexural strengths in 0° and 90° directions were determined relative to the 0° direction of the surface layer of the obtained flat plate, the average value of the flexural strengths in 0° and 90° directions was 485 MPa, the fiber strength utilization factor was 16.2 MPa/%, and the CV value was less than 5%.

When a sample having a size of 100 mm×100 mm was cut out from the obtained flat plate and the flow test was performed, a good article could be obtained in which flowability in the flow test was 270%. The conditions and the results of the determinations and the evaluations are shown in Table 1.

Example 2

Example 2 was performed in a manner similar to that of Example 1 other than the conditions where a carbon fiber nonwoven fabric was formed in which the proportion of the carbon fiber bundles (1) relative to the total weight of carbon fibers in the carbon fiber nonwoven fabric was 40 wt. %, the number average x of carbon fibers forming the bundle was 320, and the standard deviation σ was 200. When the flexural strengths in 0° and 90° directions and flowability of the obtained flat plate were determined, a good article could be obtained in which the average value of the flexural strengths in 0° and 90° directions was 480 MPa, the fiber strength utilization factor was 16.0 MPa/%, the CV value was less than 5%, and flowability was 290%.

Example 3

Example 3 was performed in a manner similar to that of Example 1 other than the conditions where a carbon fiber nonwoven fabric was formed in which the proportion of the carbon fiber bundles (1) relative to the total weight of carbon fibers in the carbon fiber nonwoven fabric was 62 wt. %, the number average x of carbon fibers forming the bundle was 615, and the standard deviation σ was 320. When the flexural strengths in 0° and 90° directions and flowability of the obtained flat plate were determined, a good article could be obtained in which the average value of the flexural strengths in 0° and 90° directions was 463 MPa, the fiber strength utilization factor was 15.4 MPa/%, the CV value was less than 5%, and flowability was 313%.

Examples 4-7, Comparative Examples 1-2

Flat plates comprising carbon fiber nonwoven fabrics were obtained in a manner similar to that of Example 2 other than the conditions where the carbon fiber bundle (A) was changed to the carbon fiber bundle (B), (C), (D), (E), (F) or (G) as compared to Example 2. The conditions and the results of the determinations and the evaluations are shown together in Tables 1 and 2.

Comparative Example 3

Comparative Example 3 was performed in a manner similar to that of Example 1 other than the conditions where a carbon fiber nonwoven fabric was formed in which the proportion of the carbon fiber bundles (1) relative to the total weight of carbon fibers in the carbon fiber nonwoven fabric was 84 wt. %, the number average x of carbon fibers forming the bundle was 1,100, and the standard deviation σ was 630. When the flexural strengths in 0° and 90° directions and flowability of the obtained flat plate were determined, the average value of the flexural strengths in 0° and 90° directions was 300 MPa, the fiber strength utilization factor was 10.0 MPa/%, the CV value was not less than 5%, and flowability was 320%, and although flowability was excellent, the flexural strength and the fiber strength utilization factor were low, the mechanical properties were poor and the variability thereof was great.

TABLE 1 Example 1 2 3 4 5 6 7 Carbon fiber bundle used before (A) (A) (A) (B) (C) (D) (E) cutting Carbon fiber cut length [mm] 15 15 15 15 15 15 15 Proportion of carbon fiber [%] 18 40 62 40 40 40 40 bundles (1) x: average value of number of [number] 180 320 615 320 320 320 320 fibers forming bundle σ: standard deviation 107 200 320 200 200 200 200 Resin CM1001 CM1001 CM1001 CM1001 CM1001 CM1001 CM1001 Vf [%] 30 30 30 30 30 30 30 Flowability [%] 270 290 313 293 291 300 293 Flexural strength (JIS-K7171) [MPa] 485 480 463 484 487 473 486 CV value ◯ ◯ ◯ ◯ ◯ ◯ ◯ Fiber strength utilization factor [MPa/%] 16.2 16.0 15.4 16.1 16.2 15.8 16.2 ◯: CV value is lower than 5%. X: CV value is 5% or higher.

TABLE 2 Comparative Example 1 2 3 Carbon fiber bundle (F) (G) (A) used before cutting Carbon fiber cut length [mm] 15 15 15 Proportion of carbon [%] 39 41 84 fiber bundles (1) x: average value [number] 314 330 1100 of number of fibers forming bundle σ: standard deviation 197 220 630 Resin CM1001 CM1001 CM1001 Vf [%] 30 30 30 Flowability [%] 280 288 320 Flexural strength [MPa] 421 417 310 (JIS-K7171) CV value ∘ ∘ x Fiber strength utilization [MPa/%] 14.0 13.9 10.3 factor ∘: CV value is lower than 5%. x: CV value is 5% or higher. Next, carbon fibers and sizing agents used in Examples 8 to 14 and Comparative Examples 4 to 6 will be explained.

Carbon Fiber Bundle (A1):

To a continuous carbon fiber bundle having a fiber diameter of 7 μm, a tensile elastic modulus of 230 GPa, a single fiber flexural stiffness of 2.71×10⁻¹¹ Pa·m⁴ and a number of filaments of 24,000, a sizing agent, prepared by setting R² in the aforementioned chemical formula (1) to —CH₂CH₂—, R³ to —CH₃, m to 2 and n to 2 and preparing a water emulsion in which the resin component of the sizing agent was 1 wt. %, was provided to the carbon fibers by dipping method, and drying was carried out at 180° C. The adhesion amount was 0.8 wt. %.

Carbon Fiber Bundle (B1):

The carbon fiber bundle was prepared in a manner similar to that in the carbon fiber bundle (A1) other than a condition where the sizing agent was changed to a sizing agent prepared by setting R² in the aforementioned chemical formula (1) to —CH₂CH₂—, R³ to —CH₃, m to 5 and n to 5.

Carbon Fiber Bundle (C1):

The carbon fiber bundle was prepared in a manner similar to that in the carbon fiber bundle (A1) other than a condition where the sizing agent was changed to a sizing agent prepared by setting R² in the aforementioned chemical formula (1) to —CH₂CH₂—, R³ to —CH₃, m to 10 and n to 10.

Carbon Fiber Bundle (D1):

The carbon fiber bundle was prepared in a manner similar to that in the carbon fiber bundle (A1) other than a condition where the sizing agent was changed to a sizing agent prepared by setting R² in the aforementioned chemical formula (1) to —CH₂CH₂—, R³ to —H, m to 15 and n to 15.

Carbon fiber bundle (E1):

The carbon fiber bundle was prepared in a manner similar to that in the carbon fiber bundle (A1) other than a condition where the sizing agent was changed to a sizing agent prepared by setting R² in the aforementioned chemical formula (1) to —CH₂CH₂—, R³ to —CH₃, m to 30 and n to 30.

Carbon Fiber Bundle (F1):

The carbon fiber bundle was prepared in a manner similar to that in the carbon fiber bundle (A1) other than a condition where the sizing agent was changed to a sizing agent prepared by setting R² in the aforementioned chemical formula (1) to —OH, R³ to —CH₃, m to 15 and n to 15.

Carbon fiber bundle (G1):

The carbon fiber bundle was prepared in a manner similar to that in the carbon fiber bundle (A1) other than a condition where the sizing agent was changed to a sizing agent prepared by setting R² in the aforementioned chemical formula (1) to —CH₂CH₂—, R³ to —CH₃, m to 1 and n to 1.

Example 8

The carbon fiber bundle (A1) was cut at a fiber length of 15 mm, the cut carbon fiber bundles (A1) and nylon 6 short fibers (fineness of short fiber: 1.7 dtex, cut length: 51 mm, number of crimps: 12 crests per 25 mm, rate of crimp: 15%) were mixed at a mass ratio of 90:10, and the mixture was introduced into a carding machine. The web having come out was cross wrapped to form a sheet-like carbon fiber nonwoven fabric comprising carbon fiber bundles (A1) and nylon 6 fibers and having an areal weight of 100 g/cm². The proportion of the carbon fiber bundles (1) relative to the total weight of carbon fibers in the carbon fiber nonwoven fabric was 18 wt. %, the number average x of carbon fibers forming the bundle was 160, and the standard deviation σ was 70.

The winding direction of the sheet-like carbon fiber nonwoven fabric was referred to as 0°, the sheets of the carbon fiber nonwoven fabrics were stacked at 0°/90° and, further, after a nylon resin film (“CM1001”, ηr=2.3, supplied by Toray Industries, Inc.) was stacked so that the volume ratio of the carbon fibers to the thermoplastic resin became 30:70 as the whole of the stacked carbon fiber nonwoven fabrics, the whole was nipped by stainless plates, and after preheating at 260° C. for 90 seconds, it was hot pressed at 260° C. for 180 seconds while being applied with a pressure of 2.0 MPa. Then, it was cooled down to 50° C. at the pressed condition to obtain a flat plate of carbon fiber composite material having a thickness of 2 mm. When the flexural strengths in 0° and 90° directions were determined relative to the 0° direction of the surface layer of the obtained flat plate, the average value of the flexural strengths in 0° and 90° directions was 467 MPa, the fiber strength utilization factor was 15.6 MPa/%, and the CV value was less than 5%.

When a sample having a size of 100 mm×100 mm was cut out from the obtained flat plate and the flow test was performed, a good article could be obtained in which flowability in the flow test was 275%. The conditions and the results of the determinations and the evaluations are shown in Table 3.

Example 9

Example 9 was performed in a manner similar to that of Example 8 other than the conditions where a carbon fiber nonwoven fabric was formed in which the proportion of the carbon fiber bundles (1) relative to the total weight of carbon fibers in the carbon fiber nonwoven fabric was 40 wt. %, the number average x of carbon fibers forming the bundle was 320, and the standard deviation σ was 200. When the flexural strengths in 0° and 90° directions and flowability of the obtained flat plate were determined, a good article could be obtained in which the average value of the flexural strengths in 0° and 90° directions was 461 MPa, the fiber strength utilization factor was 15.4 MPa/%, the CV value was less than 5%, and flowability was 297%.

Example 10

Example 10 was performed in a manner similar to that of Example 8 other than the conditions where a carbon fiber nonwoven fabric was formed in which the proportion of the carbon fiber bundles (1) relative to the total weight of carbon fibers in the carbon fiber nonwoven fabric was 62 wt. %, the number average x of carbon fibers forming the bundle was 615, and the standard deviation σ was 320. When the flexural strengths in 0° and 90° directions and flowability of the obtained flat plate were determined, a good article could be obtained in which the average value of the flexural strengths in 0° and 90° directions was 449 MPa, the fiber strength utilization factor was 15.0 MPa/%, the CV value was less than 5%, and flowability was 318%.

Examples 11-14, Comparative Examples 4-5

Flat plates comprising carbon fiber nonwoven fabrics were obtained in a manner similar to that of Example 9 other than the conditions where the carbon fiber bundle (A1) was changed to the carbon fiber bundle (B1), (C1), (D1), (E1), (F1) or (G1) as compared to Example 9 as shown in Tables 3 and 4. The conditions and the results of the determinations and the evaluations are shown together in Tables 3 and 4.

Comparative Example 6

Comparative Example 6 was performed in a manner similar to that of Example 8 other than the conditions where a carbon fiber nonwoven fabric was formed in which the proportion of the carbon fiber bundles (1) relative to the total weight of carbon fibers in the carbon fiber nonwoven fabric was 84 wt. %, the number average x of carbon fibers forming the bundle was 1,100, and the standard deviation σ was 630. When the flexural strengths in 0° and 90° directions and flowability of the obtained flat plate were determined, the average value of the flexural strengths in 0° and 90° directions was 300 MPa, the fiber strength utilization factor was 10.0 MPa/%, the CV value was not less than 5%, and flowability was 332%, and although flowability was excellent, the flexural strength and the fiber strength utilization factor were low, the mechanical properties were poor and the variability thereof was great.

TABLE 3 Example 8 9 10 11 12 13 14 Carbon fiber bundle used before (A1) (A1) (A1) (B1) (C1) (D1) (E1) cutting Number of atoms of epoxy/ 8 8 8 17 32 47 92 aromatic ring Carbon fiber cut length [mm] 15 15 15 15 15 15 15 Proportion of carbon fiber [%] 18 40 62 40 40 40 40 bundles (1) x: average value of number of [number] 180 320 615 320 320 320 320 fibers forming bundle σ: standard deviation 107 200 320 200 200 200 200 Resin CM1001 CM1001 CM1001 CM1001 CM1001 CM1001 CM1001 Vf [%] 30 30 30 30 30 30 30 Flowability [%] 275 297 318 304 295 297 300 Flexural strength (JIS-K7171) [MPa] 467 461 449 464 472 469 467 CV value ◯ ◯ ◯ ◯ ◯ ◯ ◯ Fiber strength utilization factor [MPa/%] 15.6 15.4 15.0 15.5 15.7 15.6 15.6 ◯: CV value is lower than 5%. X: CV value is 5% or higher.

TABLE 4 Comparative Example 4 5 6 Carbon fiber bundle (F1) (G1) (A1) used before cutting Number of atoms of — 5 8 epoxy/aromatic ring Carbon fiber cut length [mm] 15 15 15 Proportion of carbon [%] 39 41 84 fiber bundles (1) x: average value [number] 314 330 1100 of number of fibers forming bundle σ: standard deviation 197 220 630 Resin CM1001 CM1001 CM1001 Vf [%] 30 30 30 Flowability [%] 275 295 332 Flexural strength [MPa] 416 411 300 (JIS-K7171) CV value ∘ ∘ x Fiber strength utilization [MPa/%] 13.9 13.7 10.0 factor ∘: CV value is lower than 5%. x: CV value is 5% or higher.

Next, carbon fibers and sizing agents used in Examples 15 to 26 and Comparative Examples 7 to 9 will be explained.

Carbon Fiber Bundle (A2):

As a sizing agent, a water dispersion emulsion having a concentration of 1 wt. % of a derivative of bisphenol A ethylene oxide adduct, set in the formula (3) at R₁=OH, R₂=H, m=15 and n=15, was prepared. After a continuous carbon fiber bundle having a fiber diameter of 7 μm, a tensile elastic modulus of 230 GPa, a single fiber flexural stiffness of 2.71×10⁻¹¹ Pa·m⁴ and a number of filaments of 24,000 was dipped in this sizing agent emulsion through dip rollers, it was dried at 150° C. for 1 minute using a hot air circulation type drier. When the adhesion amount of the sizing agent, the coefficient of friction and the drape value were determined, the adhesion amount was 0.8 wt. %, the coefficient of friction was 0.22 and the drape value was 5.3 cm.

Carbon Fiber Bundle (B2):

The carbon fiber bundle was prepared in a manner similar to that in the carbon fiber bundle (A2) with respect to the used carbon fibers and the method of providing a sizing agent, other than a condition where a water dispersion emulsion having a concentration of 1 wt. % of a compound, set in the formula (3) at R₁: a compound shown as the formula (7), R₂=H, m=15 and n=15, was prepared as the sizing agent. When the adhesion amount of the sizing agent, the coefficient of friction and the drape value were determined, the adhesion amount was 0.9 wt. %, the coefficient of friction was 0.23 and the drape value was 5.5 cm.

Carbon Fiber Bundle (C2):

The carbon fiber bundle was prepared in a manner similar to that in the carbon fiber bundle (A2) with respect to the used carbon fibers and the method of providing a sizing agent, other than a condition where a water dispersion emulsion having a concentration of 1 wt. % of a compound, set in the formula (4) at R₁=H, R₂=OH, m=10 and n=10, was prepared as the sizing agent. When the adhesion amount of the sizing agent, the coefficient of friction and the drape value were determined, the adhesion amount was 0.6 wt. %, the coefficient of friction was 0.21 and the drape value was 5.0 cm.

Carbon Fiber Bundle (D2):

87 g of anisotropic object mixture of 2•4-/2•6-tolylene diisocyanate and 34.4 g of N-methyl dimethanol benzyl ammonium chloride were added to 260 g of polypropylene glycol having a hydroxyl value of 112, and it was reacted in a nitrogen atmosphere at 40° C. for 2 hours to prepare a urethane compound containing 2.23 wt. % of isocyanate group and 0.513 wt. % of quaternary nitrogen. To this, 41.3 g of glycerol diglycidyl ether and 335.4 g of DMF (dimethyl formamide) were added, it was reacted at 50° C. for about 3 hours until the isocyanate group vanished. The reaction product was one containing 0.743 g of oxirane oxygen and 0.476 g of quaternary nitrogen and exhibiting a good water dispersion property.

To the above-described polyurethane obtained, dimethyl formamide solution containing 30 wt. % of bisphenol A diglycidyl ether type liquid epoxy resin having an epoxy equivalent of 225 to 280 and an average molecular weight of about 470 (“Epikote” 843, supplied by Shell Chemicals Ltd.) was added at a rate of 4:1, then, water was added and an emulsion of 1 wt. % thereof was prepared as a sizing agent. The other conditions were similar to those for the carbon fiber bundle (A2). When the adhesion amount of the sizing agent, the coefficient of friction and the drape value were determined, the adhesion amount was 0.8 wt. %, the coefficient of friction was 0.34 and the drape value was 10.5 cm.

Carbon Fiber Bundle (E2):

The carbon fiber bundle was prepared in a manner similar to that in the carbon fiber bundle (A2) with respect to the used carbon fibers and the method of providing a sizing agent, other than a condition where a water dispersion emulsion having a concentration of 1 wt. % of a compound, set in the formula (3) at R₁=OH, R₂=H, m=1 and n=1, was prepared as the sizing agent. When the adhesion amount of the sizing agent, the coefficient of friction and the drape value were determined, the adhesion amount was 0.7 wt. %, the coefficient of friction was 0.35 and the drape value was 6.2 cm.

Example 15

The carbon fiber bundle (A2) was cut at a fiber length of 6 mm, the cut carbon fiber bundles and nylon 6 short fibers (fineness of short fiber: 1.7 dtex, cut length: 10 mm) were mixed at a mass ratio of 80:20, and the mixture was introduced into an air laid machine. The web having come out was heat treated to form a sheet-like carbon fiber nonwoven fabric comprising the carbon fibers and the nylon 6 fibers and having an areal weight of 200 g/cm². When the fiber bundles of the prepared nonwoven fabric were determined, the proportion of the carbon fiber bundles (1) relative to the total weight of carbon fibers was 13 wt. %, the number average x of carbon fibers forming the bundle was 160, and the standard deviation σ was 70.

The winding direction of the sheet-like carbon fiber aggregates was referred to as 0°, the sheets of the carbon fiber aggregates were stacked in a same direction, and after a nylon resin melt blow nonwoven fabric (“CM1001”, ηr=2.3, supplied by Toray Industries, Inc.) was stacked so that the volume ratio of the carbon fibers to the thermoplastic resin became 30:70 as the whole of the stacked carbon fiber aggregates, the whole was nipped by stainless plates, and after preheating at 260° C. for 90 seconds, it was hot pressed at 250° C. for 180 seconds while being applied with a pressure of 2.0 MPa. Then, it was cooled down to 50° C. at the pressed condition to obtain a flat plate of carbon fiber composite material having a thickness of 2 mm. When the flexural strengths in 0° and 90° directions were determined relative to the 0° direction of the surface layer of the obtained flat plate, the average value of the flexural strengths in 0° and 90° directions was 470 MPa, the fiber strength utilization factor was 15.7 MPa/%, and the CV value was less than 5%.

When a sample having a size of 100 mm×100 mm was cut out from the obtained flat plate and the flow test was performed, a good article could be obtained in which flowability in the flow test was 300%. The conditions and the results of the determinations and the evaluations are shown in Table 5.

Examples 16-26

Flat plates comprising carbon fiber nonwoven fabrics were obtained in a manner similar to that of Example 15 other than the conditions changed as compared to Example 15 as shown in Tables 5 and 6. The conditions and the results of the determinations and the evaluations are shown in Tables 5 and 6.

Comparative Example 7

A flat plate of a carbon fiber composite material comprising carbon fiber nonwoven fabrics was obtained in a manner similar to that of Example 15 other than the conditions where the carbon fiber bundle (D2) was cut at a fiber length of 15 mm, the cut carbon fiber bundles and nylon 6 discontinuous fibers (fineness of short fiber: 1.7 dtex, cut length: 10 mm) were mixed at a mass ratio of 80:20, and a carbon fiber nonwoven fabric was prepared in which the proportion of the carbon fiber bundles (1) was 23 wt. %, the number average x of carbon fibers forming the bundle was 250, and the standard deviation σ was 200. The conditions and the results of the determinations and the evaluations are shown in Table 7. The obtained carbon fiber nonwoven fabric is poor in flowability.

Comparative Example 8

A flat plate of a carbon fiber composite material comprising carbon fiber nonwoven fabrics was obtained in a manner similar to that of Example 15 other than the conditions where the carbon fiber bundle (E2) was cut at a fiber length of 15 mm, the cut carbon fiber bundles and nylon 6 discontinuous fibers (fineness of short fiber: 1.7 dtex, cut length: 10 mm) were mixed at a mass ratio of 80:20, and a carbon fiber nonwoven fabric was prepared in which the proportion of the carbon fiber bundles (1) was 22 wt. %, the number average x of carbon fibers forming the bundle was 260, and the standard deviation σ was 210. The conditions and the results of the determinations and the evaluations are shown together in Table 7. The obtained carbon fiber nonwoven fabric is poor in flowability.

Comparative Example 9

A flat plate of a carbon fiber composite material comprising carbon fiber nonwoven fabrics was obtained in a manner similar to that of Example 15 other than the conditions where the carbon fiber bundle (A2) was cut at a fiber length of 15 mm, the cut carbon fiber bundles and nylon 6 discontinuous fibers (fineness of short fiber: 1.7 dtex, cut length: 10 mm) were mixed at a mass ratio of 80:20, and a carbon fiber nonwoven fabric was prepared in which the proportion of the carbon fiber bundles (1) was 80 wt. %, the number average x of carbon fibers forming the bundle was 1,200, and the standard deviation σ was 630. The conditions and the results of the determinations and the evaluations are shown together in Table 7. Although the obtained carbon fiber nonwoven fabric is good in flowability, the fiber strength utilization factor is low and the variability in properties is great.

TABLE 5 Example 15 16 17 18 19 20 Carbon fiber bundle used before (A2) (A2) (A2) (A2) (A2) (A2) cutting Drape value/ [cm/(Pa · cm⁴)] 1.96 × 10³ 1.96 × 10³ 1.96 × 10³ 1.96 × 10³ 1.96 × 10³ 1.96 × 10³ flexural stiffness Carbon fiber cut length [mm] 6 15 15 15 15 15 Proportion of carbon fiber [%] 13 18 25 60 65 20 bundles (1) x: average value of number of [number] 160 180 250 200 400 605 fibers forming bundle σ: standard deviation 70 87 130 130 190 320 Resin CM1001 CM1001 CM1001 CM1001 CM1001 CM1001 Vf [%] 30 30 30 30 30 30 Flowability [%] 300 270 280 290 300 290 Flexural strength (JIS-K7171) [MPa] 470 470 450 450 440 430 CV value ◯ ◯ ◯ ◯ ◯ ◯ Fiber strength utilization factor [MPa/%] 15.7 15.7 15.0 15.0 14.7 14.3 ◯: CV value is lower than 5%. X: CV value is 5% or higher.

TABLE 6 Example 21 22 23 24 25 26 Carbon fiber bundle used before (A2) (A2) (A2) (B2) (B2) (C2) cutting Drape value/ [cm/(Pa · cm⁴)] 1.96 × 10³ 1.96 × 10³ 1.96 × 10³ 2.03 × 10³ 2.03 × 10³ 1.84 × 10³ flexural stiffness Carbon fiber cut length [mm] 15 15 15 15 15 15 Proportion of carbon fiber [%] 26 72 80 60 66 64 bundles (1) x: average value of number of [number] 840 550 860 200 405 395 fibers forming bundle σ: standard deviation 340 290 400 130 200 180 Resin CM1001 CM1001 CM1001 CM1001 CM1001 CM1001 Vf [%] 30 30 30 30 30 30 Flowability [%] 300 320 320 300 305 300 Flexural strength (JIS-K7171) [MPa] 410 410 390 470 460 450 CV value ◯ ◯ ◯ ◯ ◯ ◯ Fiber strength utilization factor [MPa/%] 13.7 13.7 13.0 15.7 15.3 15.0 ◯: CV value is lower than 5%. X: CV value is 5% or higher.

TABLE 7 Comparative Example 7 8 9 Carbon fiber bundle (D2) (E2) (A2) used before cutting Drape value/ [cm/(Pa · 3.87 × 10³ 2.29 × 10³ 1.96 × 10³ flexural stiffness cm⁴)] Carbon fiber cut length [mm] 15 15 15 Proportion of carbon [%] 23 22 80 fiber bundles (1) x: average value [number] 250 260 1200 of number of fibers forming bundle σ: standard deviation 200 210 630 Resin CM1001 CM1001 CM1001 Vf [%] 30 30 30 Flowability [%] 240 240 340 Flexural strength [MPa] 430 430 360 (JIS-K7171) CV value ∘ ∘ x Fiber strength utilization [MPa/%] 14.3 14.3 12.0 factor ∘: CV value is lower than 5%. x: CV value is 5% or higher.

INDUSTRIAL APPLICABILITY

The carbon fiber nonwoven fabric can be applied to manufacture of any carbon fiber reinforced molded article required with both of high flowability and mechanical properties and small variability in mechanical properties, which has not been achieved by conventional technologies. 

1.-16. (canceled)
 17. A carbon fiber nonwoven fabric including carbon fibers, wherein said carbon fibers are sized with an aliphatic compound having a plurality of epoxy groups, a number average x of carbon fibers forming a carbon fiber bundle, in which a number of carbon fibers forming a carbon fiber bundle is 90 or more, is 90 to 1,000 fibers per bundle among carbon fiber bundles in said carbon fiber nonwoven fabric, and a standard deviation σ of the number of carbon fibers forming said carbon fiber bundle is 50 to
 500. 18. A carbon fiber nonwoven fabric including carbon fibers, wherein said carbon fibers are sized with an aromatic compound having a plurality of epoxy groups in which a number of atoms present between an epoxy group and an aromatic ring is 6 or more, a number average x of carbon fibers forming a carbon fiber bundle, in which a number of carbon fibers forming a carbon fiber bundle is 90 or more, is 90 to 1,000 fibers per bundle among carbon fiber bundles in said carbon fiber nonwoven fabric, and a standard deviation σ of the number of carbon fibers forming said carbon fiber bundle is 50 to
 500. 19. The carbon fiber nonwoven fabric according to claim 17, wherein said compound having a plurality of epoxy groups is a compound having an epoxy group at each end of the longest atomic chain.
 20. The carbon fiber nonwoven fabric according to claim 19, wherein said compound having a plurality of epoxy groups is a compound having an epoxy group only at each end of the longest atomic chain.
 21. The carbon fiber nonwoven fabric according to claim 17, wherein a number of atoms of the longest atomic chain of said aliphatic compound having a plurality of epoxy groups is 20 to
 200. 22. The carbon fiber nonwoven fabric according to claim 17, wherein said aliphatic compound having a plurality of epoxy groups is at least one compound selected from the group consisting of glycerol polyglycidyl ether, diglycerol polyglycidyl ether, polyethylene glycol diglycidyl ether group and polypropylene glycol diglycidyl ether group.
 23. The carbon fiber nonwoven fabric according to claim 18, wherein said aromatic compound having a plurality of epoxy groups in which a number of atoms present between an epoxy group and an aromatic ring is 6 or more is a compound shown in chemical formula (1):

wherein R¹ is chemical formula (2):

R² represents an alkylene group having a carbon number of 2 to 30, R³ is —H or —CH₃, m and n represent an integer of 2 to 48, and m+n is 4 to
 50. 24. The carbon fiber nonwoven fabric according to claim 23, wherein said R² is —CH₂CH₂— or —CH(CH₃) CH₂—.
 25. The carbon fiber nonwoven fabric according to claim 18, wherein said aromatic compound is a condensed polycyclic aromatic compound.
 26. The carbon fiber nonwoven fabric according to claim 25, wherein a skeletal structure of said condensed polycyclic aromatic compound is naphthalene, anthracene, phenanthrene or pyrene.
 27. A carbon fiber nonwoven fabric including carbon fibers, wherein at least one compound selected from chemical formulae (3), (4) and (5) is made to adhere to said carbon fibers at an amount of 0.1 to 5.0 wt. % relative to the weight of said carbon fibers of 100 wt. %, a number average x of carbon fibers forming a carbon fiber bundle, in which a number of carbon fibers forming a carbon fiber bundle is 90 or more, is 90 to 1,000 fibers per bundle among carbon fiber bundles in said carbon fiber nonwoven fabric, and a standard deviation σ of the number of carbon fibers forming said carbon fiber bundle is 50 to 500

wherein R₁ represents H, OH, chemical formulae (6) or (7), R₂ represents H or OH, m and n represent an integer of 1 to 49, and m+n is in a range of 10 to 50


28. The carbon fiber nonwoven fabric according to claim 17, wherein said standard deviation σ of the number of carbon fibers forming said carbon fiber bundle is 50 to
 350. 29. The carbon fiber nonwoven fabric according to claim 17, wherein a proportion of said carbon fiber bundles relative to the total weight of carbon fibers is 5 to 80 wt. %.
 30. The carbon fiber nonwoven fabric according to claim 17, wherein said carbon fiber nonwoven fabric is formed from a carbon fiber bundle whose drape value (cm)/single fiber flexural stiffness (Pa·cm⁴) at 25° C. is 1.4×10³ to 4.0×10³ (cm/(Pa·cm⁴)).
 31. The carbon fiber nonwoven fabric according to claim 17, wherein a single fiber flexural stiffness of carbon fibers forming said carbon fiber nonwoven fabric is 1.0×10⁻¹¹ to 2.8×10⁻¹¹ (Pa·cm⁴).
 32. The carbon fiber nonwoven fabric according to claim 17, wherein a fiber length Ln of carbon fibers forming said carbon fiber nonwoven fabric is 3 to 50 mm.
 33. The carbon fiber nonwoven fabric according to claim 18, wherein said compound having a plurality of epoxy groups is a compound having an epoxy group at each end of the longest atomic chain.
 34. The carbon fiber nonwoven fabric according to claim 19, wherein a number of atoms of the longest atomic chain of said aliphatic compound having a plurality of epoxy groups is 20 to
 200. 35. The carbon fiber nonwoven fabric according to claim 19, wherein said aliphatic compound having a plurality of epoxy groups is at least one compound selected from the group consisting of glycerol polyglycidyl ether, diglycerol polyglycidyl ether, polyethylene glycol diglycidyl ether group and polypropylene glycol diglycidyl ether group. 